The growing use of the drug, known as crystal meth or ice, comes at a critical time. Some fear that, with the exit of most foreign troops by the end of next year and dwindling interest and aid from the international community, significant addiction to the relatively new drug could wreak social havoc.

The number of crystal meth samples taken from seizures tripled to 48 in 2012 compared with the year before, according to the United Nations Office on Drugs and Crime (UNODC).

Importantly, however, there are concerns the power vacuum left by the withdrawal of foreign troops could turn Afghanistan into a new route for moving Iranian-made crystal meth to nations in the Pacific, like Thailand and Indonesia, through Pakistan.

"It's a potential threat," a Kabul-based official from the U.S. Drug Enforcement Administration (DEA) told Reuters, speaking on condition of anonymity.

Small quantities of around half a kilogram are usually seized, said Peter Bottomley, the UNODC's consultant in Kabul, describing it as a "worrying trend".

"If this country gets addicted to meth, there will be a big problem," Bottomley said.

Afghanistan is the world's top producer of opium, from which heroin is made and which helps fund the Taliban's insurgency, and is heading for a near-record this year, the UNODC has said.

Treatment options for Afghanistan's 1 million heroin addicts, some of whom inject into their groins in broad daylight in central Kabul, are sorely limited.

In the country's sole, ultra-secretive drugs lab on the outskirts of Kabul, Afghan pharmacists analyze samples from seizures brought in on a daily basis, which are subject to three rounds of testing to identify the substance and its potency.

A sack of translucent crystals resembling large grains of sea salt sat on one of the lab's tables - one of the recent seizures of crystal meth. It stood out starkly among the brown hues of heroin, opium, morphine and hashish in tiny bags.

"If only we could get the punishment increased for selling this," said Mohammad Khalid Nabizada, the head of the lab, which operates under the Interior Ministry's Counter Narcotics Police.

Prison terms for selling crystal meth are relatively light, with dealers facing up to one year behind bars for 1 kg (2.2 lb), compared with up to three years for opium and a maximum of 10 years for the same amount of heroin.

"ABNORMAL BEHAVIOUR"

Dubbed "glass" in Afghanistan, crystal meth only appeared in recent years and is made in high-tech labs across the border in Iran. Most of it is consumed in the border provinces of Herat and Nimroz, but seizures have been scattered across the country.

Its street price is about $20, or five times that of heroin, making it relatively expensive in one of the world's poorest countries, said Ahmad Khalid Mowahid, spokesman for the Criminal Justice Task Force that convicts serious drug offenders.